CN108801713A - A kind of device for realizing the passive Collect jointly of atmospheric radioactivity tritium carbon - Google Patents
A kind of device for realizing the passive Collect jointly of atmospheric radioactivity tritium carbon Download PDFInfo
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- YZCKVEUIGOORGS-NJFSPNSNSA-N Tritium Chemical compound [3H] YZCKVEUIGOORGS-NJFSPNSNSA-N 0.000 title claims abstract description 37
- 229910052722 tritium Inorganic materials 0.000 title claims abstract description 37
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 28
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 27
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 92
- 238000005070 sampling Methods 0.000 claims abstract description 80
- 238000009792 diffusion process Methods 0.000 claims abstract description 63
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 58
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 52
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 46
- 239000003463 adsorbent Substances 0.000 claims abstract description 28
- 230000007613 environmental effect Effects 0.000 claims abstract description 19
- 239000012528 membrane Substances 0.000 claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 13
- 239000012530 fluid Substances 0.000 claims abstract description 7
- 239000000463 material Substances 0.000 claims description 42
- 238000001179 sorption measurement Methods 0.000 claims description 40
- 230000002285 radioactive effect Effects 0.000 claims description 22
- 239000011521 glass Substances 0.000 claims description 14
- 238000007789 sealing Methods 0.000 claims description 14
- 239000002808 molecular sieve Substances 0.000 claims description 11
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims description 11
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 9
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 8
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims description 8
- 239000004810 polytetrafluoroethylene Substances 0.000 claims description 8
- 239000000741 silica gel Substances 0.000 claims description 8
- 229910002027 silica gel Inorganic materials 0.000 claims description 8
- 239000000443 aerosol Substances 0.000 claims description 6
- 230000004907 flux Effects 0.000 claims description 6
- 238000004088 simulation Methods 0.000 claims description 6
- -1 Polytetrafluoroethylene Polymers 0.000 claims description 4
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- 239000000126 substance Substances 0.000 claims description 4
- 239000006096 absorbing agent Substances 0.000 claims description 3
- KVNRLNFWIYMESJ-UHFFFAOYSA-N butyronitrile Chemical compound CCCC#N KVNRLNFWIYMESJ-UHFFFAOYSA-N 0.000 claims description 3
- 238000004141 dimensional analysis Methods 0.000 claims description 3
- 230000002441 reversible effect Effects 0.000 claims description 3
- 238000012360 testing method Methods 0.000 abstract description 7
- 238000005516 engineering process Methods 0.000 abstract description 6
- 238000011835 investigation Methods 0.000 abstract description 5
- 239000002594 sorbent Substances 0.000 abstract 1
- 238000012544 monitoring process Methods 0.000 description 6
- 230000007774 longterm Effects 0.000 description 4
- 230000009897 systematic effect Effects 0.000 description 4
- 241000282414 Homo sapiens Species 0.000 description 2
- 238000009825 accumulation Methods 0.000 description 2
- 239000002156 adsorbate Substances 0.000 description 2
- 230000002860 competitive effect Effects 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
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- 238000001914 filtration Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000011002 quantification Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/02—Devices for withdrawing samples
- G01N1/22—Devices for withdrawing samples in the gaseous state
- G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
- G01N1/2214—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling by sorption
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Abstract
The invention belongs to radgas sampling technique field, it is related to a kind of new equipment that realizing the passive Collect jointly of atmospheric radioactivity tritium carbon by cap assembly, 14CO2 adsorbent chamber components, indicator chamber, HTO adsorbent chambers, diffusion chamber；Bottom cover, seal assembly and filter membrane component composition.The present invention is based on Atmospheric diffusion theory and the first diffusion principle of Fick, the efficiently concentrating realized to ambient water vapor, the carbon dioxide enriched sorbent material to work well respectively to object gas is placed in sampler；By Fluid Mechanics Computation (CFD) emulation technology, determines suitable sampling diffusion length, ensure the stability of sampling efficiency.Field test shows that the device can meet and stablizes sampling under the conditions of general environment.The device is to the acquisition of ambient water vapor and carbon dioxide without electric power support, economy, convenient, the sample acquired is 16% through measuring the result maximum relative deviation monitored with existing active devices, disclosure satisfy that the investigation demand of a wide range of environmental grade radioactivity tritium carbon.
Description
Technical Field
The invention belongs to the technical field of radioactive gas sampling, and particularly relates to a device capable of realizing passive combined sampling of atmospheric radioactive tritium and carbon.
Background
The prior art discloses3H、14C, the two most critical radionuclides, is a key target for the monitoring of radioactive contaminants in the periphery of nuclear facilities. Although it is produced by spontaneous decaythe beta rays cannot directly bring extra external irradiation harm to human beings due to low energy, but the two types of nuclear isotopes have strong exchange capacity, can replace stable isotopes of hydrogen and carbon in substances, are absorbed into human bodies through modes of food chain transfer, air suction and the like, and cause internal irradiation harm3H、14Important storage media and transport channels for C compounds, in the atmosphere3H、14Region of reaction of concentration pair of C compound3H、14C concentration level distribution and evaluation3H、14The public radiation hazard caused by C has important reference significance. Practice shows that, for long-term continuous monitoring of multiple locations, although active sampling equipment can collect samples required for measurement in a short time, the price of a sampling device is high, the sampling device also needs electric power support, and the conditions such as manpower and field limit, so that the active sampling is difficult to meet the requirements of multiple locations and long-term continuous sampling. Therefore, there is a need for further research and development of passive accumulation type with the advantages of low price, convenient use, and no need of electric power3H、14C level monitoring and atmosphere sampling device or utensil to satisfy the requirement of atmospheric environment radiation monitoring's many places, long-term continuous measurement. Although several passive accumulation types exist at home and abroad at present3H sampler, but ① research is not comprehensive and systematic, wherein ① main disadvantages are that ① design of ① geometric structure of ① sampler lacks reliable scientific basis, ① selection and quantification of adsorbent materials of ① sampler lack systematic basis, ① systematic discussion of influence of meteorological factors on ① acquisition performance, ① systematic consideration of influence of ① saturation characteristics of ① adsorbent materials on ① result in ① acquisition process, ① fifth consideration of ① relationship between aerosol deposition and ① orientation of ① sampling port, and ① like, so that ① key technical parameters such as ① control of ① adsorption endpoint in ① environmental application process cannot be accurately and quantitatively evaluated, and ① advantages and disadvantages and ① environmental suitability cannot be judged, research shows,3H、14the sample collection of C has similarity in theory and methodology, but no passive sampler at home and abroad can simultaneously realize the simultaneous collection of environmental radioactive tritium and carbon, and the actual requirement isWhen using, arrange two passive forms samplers at same sampling point and also will cause the waste of resource, consequently, based on prior art's current situation, the inventor of this application plans to provide a convenient to use, the accuracy is high, can be to the new installation that radioactive tritium carbon gathered passively simultaneously in the environment simultaneously, and the device can realize in the peripheral atmosphere of nuclear facility3H、14And C, conventional monitoring and emergency monitoring.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a novel device which is convenient to use, has high accuracy and can passively collect radioactive tritium and carbon in the environment. In particular to a device for realizing passive combined collection of atmospheric radioactive tritium and carbon.
Based on the atmospheric diffusion theory and the Fick first diffusion principle, adsorbent materials with good enrichment effects on environmental water vapor and carbon dioxide are placed in a sampler of the device to realize high-efficiency enrichment on target gas; through a Computational Fluid Dynamics (CFD) simulation technology, a proper sampling diffusion length is determined, and the stability of sampling efficiency is guaranteed. The field test shows that the device can meet the stable sampling under the general environmental condition. The device does not need electric power support, economy, convenience to the collection of environment vapor and carbon dioxide, and the sample of gathering is measured and is 16% with the biggest relative deviation of the result that current initiative equipment monitored, can satisfy the investigation demand of environmental level radioactivity tritium carbon on a large scale.
More specifically, the invention relates to a device for jointly sampling atmospheric radioactive tritium and carbon, which comprises: a top cover assembly 1, a 14CO2 adsorption cavity assembly 2, an indicator cavity assembly 3, an HTO adsorption cavity assembly 4 and a diffusion cavity assembly 5; a bottom cover component 6, a sealing component 7 and a filter membrane component 8.
In the top cover assembly, a lifting ring is adhered to the top cover and is suspended on a support during sampling, so that the weight of the sampler during sampling can be measured, and the assembly structure is shown in figure 1;
according to the invention14CO2The adsorption cavity assembly is shown in figure 1 and is structurally a hollow organic glass cylinder, a mat wire mesh is bonded at the upper end of the hollow organic glass cylinder, and the wire mesh can bear an adsorbent material; arranging a quantitative carbon dioxide adsorbing material (13X molecular sieve) in the cylinder during sampling;
the adsorption indication cavity assembly is shown in figure 1 and is structurally an organic glass hollow cylinder, a layer of mat wire mesh is bonded at the upper end of the hollow cylinder, and the wire mesh can bear adsorbent materials; during sampling, a certain amount of indicator material (anhydrous allochroic silica gel) is arranged in the cylinder, when the adsorption efficiency of the 3A molecular sieve in the HTO adsorption cavity assembly of the sampler is reduced due to adsorption saturation, the anhydrous allochroic silica gel can continuously absorb water, and the color change of the allochroic silica gel reflects the color change of the sampler14CO2According to the humidity condition in the adsorption cavity assembly, the 13X molecular sieve can simultaneously adsorb water vapor and carbon dioxide in the atmosphere, and two adsorbates have a competitive relationship in the adsorption process, so that the carbon dioxide adsorption layer needs to be ensured to be dry as much as possible, and the adsorption influence of 13X on the water vapor is reduced;
the structure of the HTO adsorption cavity component is shown in figure 1, and the HTO adsorption cavity component is an organic glass hollow cylinder, a mat wire mesh is bonded at the upper end of the hollow cylinder, a certain amount of adsorbent materials (3A molecular sieves) are arranged in the cylinder during sampling, and the wire mesh can bear the weight of the adsorbent materials;
the diffusion cylinder assembly can simultaneously collect HTO and HTO in the environment14CO2Reasonably optimizing the diffusion length of the sampler by a CFD (computational fluid dynamics) simulation technology, and determining the geometric dimension of the diffusion area of the sampler as follows: the specific inner diameter, outer diameter and length of the sampler can basically eliminate the influence of wind field turbulence on the adsorption efficiency of the sampler;
the bottom cover assembly is basically the same as the top cover assembly, and for different sampling requirements, three types of bottom covers are designed, namely small-hole bottom covers, and the bottom cover assembly is suitable for being used under the condition of high environmental humidity during sampling; a large pore bottom cover, adapted for use in situations of low ambient humidity during sampling; the bottom cover without the hole is suitable for being used under the condition that the sampler is transferred back to a laboratory or needs to be stored after the sampling is finished;
the seal assembly of the present invention: the design of a sealing ring is adopted at each spiral connection part, the size of the sealing ring is 80mm in inner diameter, 87mm in outer diameter and 1mm in thickness, and the sealing ring is made of butyronitrile, so that the connection part is sealed as much as possible;
the filter membrane component adopts a Polytetrafluoroethylene (PTFE) hydrophobic membrane, so that aerosol and water drops in the environment can be isolated during sampling, and the water can only pass through in the form of gaseous water molecules in the sampling process.
In the embodiment of the invention, considering the scheme that the sampling opening is arranged upwards, aerosol and water drops in the environment can be deposited on the sampling filter membrane during sampling, which affects the stability of sampling efficiency, so that a suspended sampler structure is designed, the geometric dimension of the sampler is reasonably optimized through a CFD (computational fluid dynamics) simulation technology, the proper diffusion length is determined, and the stable collection of water vapor and carbon dioxide under general environmental conditions (the temperature condition is 5-40 ℃, the humidity condition is 15-90% RH, and the wind speed condition is 0.1-4.5 m/s) can be met.
The device carries out on-site sampling test, and comprises that based on the atmospheric diffusion principle, an adsorption material with better enrichment effect on environmental water vapor and carbon dioxide is arranged in a sampler of the device, so that concentration difference of the water vapor and the carbon dioxide inside and outside the sampler is promoted; according to the Fick's first diffusion law, water vapor molecules and carbon dioxide molecules with higher concentration in the environment diffuse to the surface of the adsorbing material (the water vapor adsorbing material is a 3A molecular sieve, and the carbon dioxide adsorbing material is a 13X molecular sieve) in the sampler along the concentration gradient, an area with relatively stable air flow and only molecular diffusion is formed between the external air and the surface of the material, and the water vapor molecules passing through the sampling holes are ensured to pass through the stable area in a diffusion manner and be adsorbed on the enrichment surface.
The diffusion flux in the above process is proportional to the concentration gradient of the substance, the molecular diffusion coefficient, and inversely proportional to the length of the diffusion layer, and can be described as:
J＝-D×dC/dx (1)
in the formula: j is diffusion flux, g.s-1·m-2(ii) a D is the diffusion coefficient, m2·s-1；dC/dx，g·m-4Is a concentration gradient; the minus sign indicates that the diffusion direction is the reverse concentration gradient direction, i.e. the diffusion material is diffused from the high concentration region to the low concentration region;
after a period of passive collection, the quality of the sample collected in the sampler is as follows:
△W＝J×S×T×86400 (2)
wherein, Delta W is the mass of water vapor (mass of carbon dioxide) collected by the adsorbent, g, S is the collection surface area, m2(ii) a T is the number of sampling days, d; 86400 is a time dimension conversion coefficient.
Assuming that the adsorbent in the sampler is an ideal absorber, i.e. the water vapor and carbon dioxide entering the sampler are completely absorbed, and the effective diffusion length of the sampler does not change with the expansion of the adsorbent, i.e. equation (2) changes:
△W＝D×Hair×S×T/δ (3)
in the formula: hairThe sample concentration (water vapor concentration, g · m) of the air around the sampler-3(ii) a Carbon dioxide concentration, ppm), delta is the effective diffusion length, m
let η be D S/δ, where η is a parameter that is the same as the unit of sampling efficiency as measured by dimensional analysis, and the shape S/δ is constant for a particular sampler, so the theoretical sampling rate is only a constant related to the sample diffusion coefficient D.
Due to the HTO in the environment,14CO2Mixed with water vapor and carbon dioxide, so that the average concentration level of tritium in air can be obtained by measuring the concentration of tritium in the collected water vapor, and similarly, the average concentration level of tritium in the collected carbon dioxide can be obtained by measuring the concentration of tritium in the collected carbon dioxide14The concentration of C can be obtained in the air14Average concentration of C:
Ca＝A/(η×T) (4)
in the formula: caIn the air3H/14Average concentration level of C, Bq. m-3A is the radioactivity of the collected sample, Bq, η is the equivalent sampling efficiency, m3·d-1。
The result of the field sampling test shows that the device can meet the stable sampling under the general environmental conditions (the temperature condition is 5-40 ℃, the humidity condition is 15-90 percent, and the wind speed condition is 0.1-4.5 m/s). The device does not need electric power support, economy, convenience to the collection of environment vapor and carbon dioxide, and the sample of gathering is measured and is 16% with the biggest relative deviation of the result that current initiative equipment monitored, can satisfy the investigation demand of environmental level radioactivity tritium carbon on a large scale. The invention has the advantages that:
the device is a passive sampler which can be used in the field so far and can simultaneously collect radioactive tritium carbon in the atmosphere, the sampler is low in manufacturing cost, easy to arrange and free from external power support, the requirement of long-time large-range environmental tritium carbon level investigation can be met, and the device can be further used for researching the long-term influence of nuclear facilities on the surrounding environment.
Drawings
FIG. 1 is a schematic diagram of a device for combined sampling of atmospheric radioactive tritium and carbon,
wherein: 1, a top cover assembly; 2, 14CO2 adsorption chamber components; 3 an indicator chamber assembly; 4HTO adsorption chamber assembly; 5 a diffusion chamber assembly; 6 bottom cap cavity assembly; 7 sealing the assembly; 8, filtering membrane component.
Detailed Description
Example 1 apparatus for passive combined collection of atmospheric radioactive tritium and carbon
As shown in fig. 1, the apparatus for preparing the atmospheric radioactive tritium-carbon combined sampling of the present invention comprises: a top cover assembly 1, a 14CO2 adsorption cavity assembly 2, an indicator cavity assembly 3, an HTO adsorption cavity assembly 4 and a diffusion cavity assembly 5; a bottom cover component 6, a sealing component 7 and a filter membrane component 8. Wherein,
the top cover component: a lifting ring is bonded on the top cover and is suspended on the support during sampling, so that the weight (3-4 kg) of the sampler during sampling can be measured;
14CO2an adsorption cavity component: the structure of the device is an organic glass hollow cylinder with the inner diameter of 80mm, the outer diameter of 100mm and the length of 90mm, a layer of 200-mesh mat wire mesh with the diameter of 82mm is bonded at the upper end of the hollow cylinder, the wire mesh can bear adsorbent materials, and a certain amount of carbon dioxide adsorption materials (13X molecular sieves) are arranged in the cylinder during sampling;
adsorbing the indication cavity assembly: the structure of the adsorbent is a hollow organic glass cylinder with the inner diameter of 80mm, the outer diameter of 100mm and the length of 90mm, a layer of mat wire mesh with the diameter of 82mm and the mesh of 200 meshes is bonded at the upper end of the hollow cylinder, and the mesh of the mat wire mesh can bear the adsorbent material. During sampling, a certain amount of indicator material (anhydrous allochroic silica gel) is arranged in the cylinder, when the adsorption efficiency of the 3A molecular sieve in the HTO adsorption cavity assembly of the sampler is reduced due to adsorption saturation, the anhydrous allochroic silica gel can continuously absorb water, and the color change of the allochroic silica gel reflects the color change of the sampler14CO2Under the condition of humidity in the adsorption cavity assembly, the 13X molecular sieve can simultaneously adsorb water vapor and carbon dioxide in the atmosphere, and two adsorbates have a competitive relationship in the adsorption process, so that the carbon dioxide adsorption layer is ensured to be dry as much as possible, and the adsorption influence of 13X on the water vapor is reduced;
HTO adsorption chamber assembly: the structure of the device is an organic glass hollow cylinder with the inner diameter of 80mm, the outer diameter of 100mm and the length of 130mm, a layer of 200-mesh mat wire mesh with the diameter of 82mm is bonded at the upper end of the hollow cylinder, a certain amount of adsorbent material (3A molecular sieve) is arranged in the cylinder during sampling, and the wire mesh can bear the weight of the adsorbent material;
a diffuser assembly: is made to simultaneously collect HTO and HTO in the environment14CO2The passive sampler of (1) reasonably optimizes the diffusion length of the sampler by a CFD (computational fluid dynamics) simulation technology, and determines the geometric dimension of the diffusion area of the sampler as follows: the inner diameter is 80mm, the outer diameter is 100mm, the length is 200mm, and the influence of wind field turbulence on the adsorption efficiency of the sampler can be basically eliminated;
the bottom cover component is basically the same as the top cover component, and three types of bottom covers are designed for different sampling requirements, wherein the first type is an openingThe small hole bottom cover is suitable for being used under the condition that the environmental humidity is higher during sampling, and the second type is an open holeThe third is a bottom cover without an opening, and is suitable for being used under the condition that the sampler is transferred back to a laboratory or the sampler needs to be stored after sampling is finished;
a sealing component: considering that the connection port of the sampler is sealed as much as possible, the design of a sealing ring is adopted at each spiral connection position, the size of the sealing ring is 80mm in inner diameter, 87mm in outer diameter and 1mm in thickness, and the material is butyronitrile;
and (3) filter membrane assembly: a Polytetrafluoroethylene (PTFE) hydrophobic film is selected, so that aerosol and water drops in the environment can be isolated during sampling, and water can only pass through in the form of gaseous water molecules during sampling.
EXAMPLE 2 in situ sampling test
In the embodiment of the invention, considering the scheme that the sampling opening is arranged upwards, aerosol and water drops in the environment can be deposited on the sampling filter membrane during sampling, which affects the stability of sampling efficiency, so that a suspended sampler structure is designed, the geometric dimension of the sampler is reasonably optimized through a CFD (computational fluid dynamics) simulation technology, and the proper diffusion length is determined so as to meet the stable collection of water vapor and carbon dioxide under the general environmental conditions (the temperature condition is 5-40 ℃, the humidity condition is 15-90% RH, and the wind speed condition is 0.1-4.5 m/s).
And (3) field sampling test: an adsorbing material with a good enriching effect on environmental water vapor and carbon dioxide is arranged in a sampler of the device, so that concentration difference of the water vapor and the carbon dioxide inside and outside the sampler is promoted; according to Fick's first diffusion law, water vapor molecules and carbon dioxide molecules with higher concentration in the environment diffuse to the surface of an adsorbing material (the water vapor adsorbing material is a 3A molecular sieve, and the carbon dioxide adsorbing material is a 13X molecular sieve) in the sampler along the concentration gradient, an area with relatively stable air flow and only molecular diffusion is formed on the surface of the external air and the material, and the water vapor molecules passing through the sampling holes are ensured to pass through the stable area in a diffusion manner and be adsorbed on the enrichment surface;
the diffusion flux in the above process is proportional to the concentration gradient of the substance, the molecular diffusion coefficient, and inversely proportional to the length of the diffusion layer, and can be described as:
J＝-D×dC/dx (1)
in the formula: j is diffusion flux, g.s-1·m-2(ii) a D is the diffusion coefficient, m2·s-1；dC/dx，g·m-4Is a concentration gradient; the minus sign indicates that the diffusion direction is the reverse concentration gradient direction, i.e. the diffusion material is diffused from the high concentration region to the low concentration region;
after a period of passive collection, the quality of the sample collected in the sampler is as follows:
△W＝J×S×T×86400 (2)
wherein, Delta W is the mass of water vapor (mass of carbon dioxide) collected by the adsorbent, g, S is the collection surface area, m2(ii) a T is the number of sampling days, d; 86400 is a time dimension conversion coefficient.
Assuming that the adsorbent in the sampler is an ideal absorber, i.e. the water vapor and carbon dioxide entering the sampler are completely absorbed, and the effective diffusion length of the sampler does not change with the expansion of the adsorbent, i.e. equation (2) changes:
△W＝D×Hair×S×T/δ (3)
in the formula: hairThe sample concentration (water vapor concentration, g · m) of the air around the sampler-3(ii) a Carbon dioxide concentration, ppm), delta is the effective diffusion length, m
let η be D S/δ, where η is a parameter that is the same as the unit of sampling efficiency as measured by dimensional analysis, and the shape S/δ is constant for a particular sampler, so the theoretical sampling rate is only a constant related to the sample diffusion coefficient D.
Due to the HTO in the environment,14CO2Mixed with water vapor and carbon dioxide, so that the average concentration level of tritium in air can be obtained by measuring the concentration of tritium in the collected water vapor, and similarly, the average concentration level of tritium in the collected carbon dioxide can be obtained by measuring the concentration of tritium in the collected carbon dioxide14The concentration of C can be obtained in the air14Average concentration of C:
Ca＝A/(η×T) (4)
in the formula: caIn the air3H/14Average concentration level of C, Bq. m-3A is the radioactivity of the collected sample, Bq, η is the equivalent sampling efficiency, m3·d-1。
The result of the field sampling test shows that the device can meet the stable sampling under the general environmental conditions (the temperature condition is 5-40 ℃, the humidity condition is 15-90 percent, and the wind speed condition is 0.1-4.5 m/s). The device does not need electric power support, economy, convenience to the collection of environment vapor and carbon dioxide, and the sample of gathering is measured and is 16% with the biggest relative deviation of the result that current initiative equipment monitored, can satisfy the investigation demand of environmental level radioactivity tritium carbon on a large scale.
Claims (10)
1. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon is characterized by comprising a top cover assembly (1), a 14CO2 adsorption cavity assembly (2), an indicator cavity assembly (3), an HTO adsorption cavity assembly (4) and a diffusion cavity assembly (5); the bottom cover component (6), the sealing component (7) and the filter membrane component (8);
in the top cover assembly, a top cover is adhered with a hanging ring; said14CO2The adsorption cavity assembly is structurally an organic glass hollow cylinder, and the upper end of the hollow cylinder is bonded with a layer of mat wire mesh which can bear the weight of an adsorbent material; the adsorption fingerThe cavity display component is structurally an organic glass hollow cylinder, and a mat wire mesh is bonded at the upper end of the hollow cylinder; the structure of the HTO adsorption cavity assembly is an organic glass hollow cylinder, and a layer of mat silk screen is bonded at the upper end of the organic glass hollow cylinder; the diffusion cylinder assembly simultaneously collects HTO and HTO in the environment14CO2Reasonably optimizing the sampler diffusion length of the device by Computational Fluid Dynamics (CFD) simulation techniques, determining the geometry of the diffusion region of the sampler of the device: the bottom cover assembly is provided with a small-hole bottom cover, a large-hole bottom cover and a bottom cover without holes; in the sealing assembly, the sealing ring design is adopted at each spiral connection part, and the material is butyronitrile; the filter membrane component is a Polytetrafluoroethylene (PTFE) hydrophobic membrane.
2. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon according to claim 1,
the lifting ring is adhered to the top cover of the top cover assembly (1), and is suspended on the support during sampling, so that the weight of the sampler during sampling is weighed.
3. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon according to claim 1,
in the 14CO2 adsorption cavity component (2), a quantitative carbon dioxide adsorption material 13X molecular sieve is arranged in the organic glass hollow cylinder during sampling;
the indicator cavity assembly (3) is characterized in that a certain amount of indicator material anhydrous allochroic silica gel is arranged in the organic glass hollow cylinder during sampling;
color change reflection sampler of color-changing silica gel14CO2And the 13X molecular sieve simultaneously adsorbs water vapor and carbon dioxide in the atmosphere under the condition of humidity in the adsorption cavity assembly.
4. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon according to claim 1,
and the HTO adsorption cavity component (4) arranges a quantitative adsorbent material 3A molecular sieve in the organic glass hollow cylinder during sampling.
5. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon according to claim 1,
the inner diameter of the diffusion cavity component (5) is 80mm, the outer diameter is 100mm, and the length is 200 mm.
6. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon according to claim 1,
in the bottom cover component (6), a small hole is formed in the bottom coverOpening of the big hole bottom cover
7. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon according to claim 1,
the size of the sealing ring in the sealing component (7) is 80mm in inner diameter, 87mm in outer diameter and 1mm in thickness.
8. The device for realizing the passive combined collection of atmospheric radioactive tritium and carbon according to claim 1,
the Polytetrafluoroethylene (PTFE) hydrophobic membrane in the filter membrane component (8) isolates aerosol and water drops in the environment during sampling, so that water only passes through in the form of gaseous water molecules during sampling.
9. A sampling method of the device for realizing the passive combined collection of atmospheric radioactive tritium and carbon based on claim 1 is characterized in that based on the atmospheric diffusion principle, an adsorbing material with a good enriching effect on environmental water vapor and carbon dioxide is arranged in a sampler of the device, so that concentration difference of the water vapor and the carbon dioxide inside and outside the sampler is promoted; according to Fick's first diffusion law, water vapor molecules and carbon dioxide molecules with higher concentration in the environment diffuse to the surface of an adsorbing material (the water vapor adsorbing material is a 3A molecular sieve, the carbon dioxide adsorbing material is a 13X molecular sieve) in the sampler along the concentration gradient, an area with relatively stable air flow and only molecular diffusion is formed on the surface of the external air and the material, and the water vapor molecules passing through the sampling holes pass through the stable area in a diffusion mode and are adsorbed on the enrichment surface;
the diffusion flux in the above process is proportional to the concentration gradient of the substance, the molecular diffusion coefficient, and inversely proportional to the length of the diffusion layer, and is described as:
J＝-D×dC/dx (1)
in the formula: j is diffusion flux, g.s-1·m-2(ii) a D is the diffusion coefficient, m2·s-1；dC/dx，g·m-4Is a concentration gradient; the minus sign indicates that the diffusion direction is the reverse concentration gradient direction, i.e. the diffusion material is diffused from the high concentration region to the low concentration region;
after a period of passive collection, the quality of the sample collected in the sampler is as follows:
△W＝J×S×T×86400 (2)
wherein, Delta W is the mass of water vapor (mass of carbon dioxide) collected by the adsorbent, g, S is the collection surface area, m2(ii) a T is the number of sampling days, d; 86400 is a time dimension conversion coefficient;
assuming that the adsorbent in the sampler is an ideal absorber, i.e. the water vapor and carbon dioxide entering the sampler are completely absorbed, and the effective diffusion length of the sampler does not change with the expansion of the adsorbent, i.e. equation (2) changes:
△W＝D×Hair×S×T/δ (3)
in the formula: hairThe sample concentration (water vapor concentration, g · m) of the air around the sampler-3(ii) a Carbon dioxide concentration, ppm), delta is the effective diffusion length, m,
let η be D S/δ, it can be known through dimensional analysis that η is a parameter that is the same as the unit of sampling efficiency, for a particular sampler, its shape S/δ is constant, and the theoretical sampling rate is only a constant related to the sample diffusion coefficient D;
based on the HTO in the environment,14CO2Mixing with vapor and carbon dioxide, measuring tritium concentration in vapor to obtain average concentration level of tritium in air, and measuring tritium concentration in carbon dioxide14The concentration of C can be obtained in the air14Average concentration of C:
Ca＝A/(η×T) (4)
in the formula: caIn the air3H/14Average concentration level of C, Bq. m-3A is the radioactivity of the collected sample, Bq, η is the equivalent sampling efficiency, m3·d-1。
10. The sampling method of claim 9, wherein the adsorbent material in the sampler comprises a 3A molecular sieve as the water vapor adsorbent material and a 13X molecular sieve as the carbon dioxide adsorbent material.
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